A method of this type and a device for carrying out the separation process are used in practice for example for separating or splitting wafers, glass substrates and plates. Substrates of this type are also used for example as interposers for electrically connecting the terminals of a plurality of homogeneous or heterogeneous microchips.
In practice, separation by cutting is a critical step in the processing of wafers or glass substrates, which is typically based on the use of diamond cutting tools and carried out for example at a speed of 30 cm/s for displays. However, the quality of the edges which can be achieved by this process is unsatisfactory, and leads to significant drawbacks in terms of the service life, quality and reliability of the product, but also in the resulting cleaning costs.
In this context, it is found to be a challenge to process the substrate into usable elements. The prior art has not yet addressed, in particular, the economical production of the plurality of separating faces in a substrate for example in the production of wafers.
US 2013/126573 A1 discloses a separating method for producing a substrate in which the substrate is irradiated with one or more pulses of a focused laser beam. In this context, the substrate is transparent to the focused laser beam, whilst the laser pulses are selected in such a way, in terms of the energy and pulse duration, that a duct-like filament is produced within the substrate. By displacing the substrate relative to the focused laser beam, additional, spatially separated filaments are produced, which thus define a separating face. The substrate consists for example of glass, crystal, quartz, diamond or sapphire. For a corresponding material thickness of the substrate, a plurality of focal points of the focused laser beam are selected in such a way that filaments are produced in at least one of the two or more layers. In this context, the filament produced by the focused laser beam in a first layer should propagate into at least one additional layer and produce a second filament in this further layer. Further, it may also be provided for a second beam focus to be produced in a second layer. In this method, the use of comparatively expensive femtosecond or picosecond lasers and the complex configuration, in which a pulse sequence of individual pulses and of particular repetition rates of the pulse sequences in accordance with particular prescriptions is provided, are found to be disadvantageous. In particular, a time delay between successive pulses in the pulse sequence is smaller than a duration of the relaxation of a material modification.
The term “stealth dicing” refers to a laser machining method in which in a first step a laser beam acts on a layer within a substrate. In a second step a tensile stress is applied so as to separate the substrate along the action points in the layer. This layer is an internal surface in the wafer, which is modified by the laser within the substrate during the processing and forms the starting point for dividing the substrate during the processing. The tensile stress subsequently brings about the separation of the substrate into small portions.
A method of this type for separating a substrate, for example a semiconductor substrate in the production of a semiconductor component or the like, is known for example from U.S. Pat. No. 8,518,800 B2. In this context, the substrate is irradiated with laser light in such a way that a multiphoton absorption phenomenon is produced within the substrate, whereby a light convergence point and thus a modified area are formed within the substrate. By forming a cutting onset point region within the substrate, a break is produced in the substrate in the direction of the thickness extent thereof, without external action or whilst exerting a force, starting from the cutting onset point region which acts as the starting point.
EP 2 503 859 A1 further discloses a method in which a glass substrate is provided with through-holes, the glass substrate consisting of an insulator such as glass, for example silicate glass, sapphire, plastics material or ceramic and semiconductors such as silicon. The glass substrate is irradiated using a laser, for example a femtosecond laser, which is focused on a focal point at a desired position within the glass substrate. The through-holes are produced by a method in which the regions of the glass substrate which have been modified by the laser are dipped in an etching solution and the modified regions are thus removed from the glass substrate. This etching makes use of the effect whereby the modified region is etched extremely rapidly by comparison with the unmodified regions of the glass substrate. Blind holes or through-openings can be produced in this manner. A copper solution is suitable for filling the through-opening. To achieve a desired depth effect, in other words a through-hole between the outer substrate faces, the focal point has to be displaced during continuous irradiation, in other words tracked in the direction of the z-axis.
More generally, the combination of selective laser treatment with a subsequent etching process in the form of selective laser-induced etching is also known as ISLE (in-volume selective laser-induced etching).
DE 10 2010 025 966 B4 further discloses a method in which in a first step focused laser pulses are directed onto the glass substrate, the radiation intensity of said pulses being high enough to result in local athermal decomposition along a filament-like track in the glass. In a second method step, the filament-like tracks are expanded into holes by supplying high-voltage power to opposing electrodes, resulting in dielectric breakdowns through the glass substrate along the filament-like tracks. These breakdowns expand under electrothermal heating and evaporation of hole material, until the process is halted by switching off the power supply upon achieving the desired hole diameter. Alternatively or in addition, the tracks may also be expanded using reactive gases, which are directed onto the hole sites using nozzles. The through-opening sites may also be expanded using supplied etching gas. The comparatively complex process, resulting from the fact the glass substrate initially has to be broken through by the athermal decomposition and the diameter of the filament-like tracks has to be expanded into holes in the following step, has proved to be disadvantageous.
Further, U.S. Pat. No. 6,400,172 B1 discloses the introduction of through-openings in semiconductor materials by laser.